1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a silicone polymer insulation film on a semiconductor substrate and a method for forming the film by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique attracts a great deal of attention. In these multi-layered structures, however, capacitance among individual wires hinders high speed operations. In order to reduce the capacitance it is necessary to reduce the dielectric constant (relative permittivity) of the insulation film. Thus, various materials having a relatively low dielectric constant have been developed for insulation films.
Conventional silicon oxide films SiOx are produced by a method in which oxygen O2 or nitrogen oxide N2O is added as an oxidizing agent to a silicon material gas such as SiH4 or Si(OC2H5)4 and then processed by heat or plasma energy. Its dielectric constant is about 4.0.
Alternatively, a fluorinated amorphous carbon film has been produced from CxFyHz as a material gas by a plasma CVD method. Its dielectric constant ∈ is as low as 2.0-2.4.
Another method to reduce the dielectric constant of an insulation film has been made by using the good stability of Sixe2x80x94O bond. A silicon-containing organic film is produced from a material gas under low pressure (1 Torr) by the plasma CVD method. The material gas is made from P-TMOS (phenyl trimethoxysilane, formula 1), which is a compound of benzene and silicon, vaporized by a babbling method. The dielectric constant ∈ of this film is as low as 3.1. 
A further method uses a porous structure made in the film. An insulation film is produced from an inorganic SOG (spin-on glass) material by a spin-coat method. The dielectric constant ∈ of the film is as low as 2.3.
However, the above noted approaches have various disadvantages as described below.
First, the fluorinated amorphous carbon film has lower thermal stability (370xc2x0 C.), poor adhesion with silicon-containing materials and also lower mechanical strength. The lower thermal stability leads to damage under high temperatures such as over 400xc2x0 C. Poor adhesion may cause the film to peel off easily. Further, the lower mechanical strength can jeopardize wiring materials.
Oligomers that are polymerized using P-TMOS molecules do not form a linear structure in the vapor phase, such as a siloxane structure, because the P-TMOS molecule has three Oxe2x80x94CH3 bonds. The oligomers having no linear structure cannot form a porous structure on a Si substrate, i.e., the density of the deposited film cannot be reduced. As a result, the dielectric constant of the film cannot be reduced to a desired degree.
In this regard, the babbling method means a method wherein vapor of a liquid material, which is obtained by having a carrier gas such as argon gas pass through the material, is introduced into a reaction chamber with the carrier gas. This method generally requires a large amount of a carrier gas in order to cause the material gas to flow. As a result, the material gas cannot stay in the reaction chamber for a sufficient length of time to cause polymerization in a vapor phase.
Further, the SOG insulation film of the spin-coat method has a problem in that the material cannot be applied onto the silicon substrate evenly and another problem in which a cure system after the coating process is costly.
It is, therefore, a principal object of this invention to provide an improved insulation film and a method for forming it.
It is another object of this invention to provide an insulation film that has a low relative constant, high thermal stability, high humidity-resistance and high adhesive strength, and a method for forming it.
It is a further object of this invention to provide a material for forming an insulation film that has a low dielectric constant, high thermal stability, high humidity-resistance and high adhesive strength.
It is a still further object of this invention to provide a method for easily forming an insulation film that has a low dielectric constant without requiring an expensive device.
One aspect of this invention involves a method for forming an insulation film on a semiconductor substrate by using a plasma CVD apparatus including a reaction chamber, which method comprises a step of vaporizing a silicon-containing hydrocarbon compound expressed by the general formula Sixcex1Oxcex2CxHy (xcex1=3, xcex2=3 or 4, x, and y are integers) and then introducing it to the reaction chamber of the plasma CVD apparatus, a step of introducing an additive gas, the flow volume of which is substantially reduced, into the reaction chamber and also a step of forming an insulation film on a semiconductor substrate by plasma polymerization reaction wherein mixed gases made from the vaporized silicon-containing hydrocarbon compound as a material gas and the additive gas are used as a reaction gas. It is a remarkable feature that the reduction of the additive gas flow also results in a substantial reduction of the total flow of the reaction gas. According to the present invention, a silicone polymer film having a micropore porous structure with low dielectric constant can be produced.
The present invention is also drawn to an insulation film formed on a semiconductor substrate, and a material for forming the insulation film, residing in the features described above.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.
In the present invention, the compound having the following formula is preferable. 
wherein n and m are any integers, and R1 to R7 are hydrocarbons (preferably n and m are independently an integer of 1 to 3, more preferably 1, and each hydrocarbon has 1 to 6 carbon atoms, more preferably one carbon atom).